[GreenKeys] FAA Teletypewriter Network 1959

[Harold Hallikainen]

> On Fri, 2 Oct 2020, Harold Hallikainen wrote:
>
>> All those circuit miles are interesting. I wonder if they ran DC loops
>> out
>> to the FSS or if they ran modems. Also, they must have had an
>> interesting
>> switching system to get data where it was supposed to go.
>>
> I don't know, but I expect the telcos used different things depending on
> their needs.  The classical circuit, such as used along railroads, is a
> single loop that loops through all the stations.  When you get away from
> railroads the telcos have to simulate that kind of circuit, running DC
> loops from the company office to the customer, and DC loops or carrier
> channels to make up the entire inter-city system.  So there are
> telegraph repeaters in the central offices to make the system work as if
> it were a single loop through all the stations.  You can see some of this
> stuff in Western Union Technical Review, and in Bell System publications.
> Then for connections from the central office to the customer Bell
> sometimes used DC loops and sometimes used modems consisting of
> individual channels of 43A1 carrier systems.
>

Thanks! When I worked in radio stations, there was a Lenkurt (I think)
demodulator under our Teletype 15RO wire service machine. You could listen
to the line and hear a bunch of AFSK signals for the different services.
The radio station got 5 bit data. My school newspaper got 6 bit to punch
tape to drive their Linotype.

I also recently read some stuff in the Mountain States Telephone and
Telegraph Company Monitor about multiplex telegraph. This was in 1919 or
so. See
http://hallikainen.org/cgi-bin/texis.cgi/webinator/search/?pr=MttMonitor&query=multiplex&submit=Submit
.

Your description of what they went through for message routing is amazing.
The invention of packet switching (and computers to handle it) sure
simplified things! But I can imagine electromechanical switching with
paper tape buffer where the entire message is a "packet" and routed based
on the address in the header. Sure easier to do in software!

Harold



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